diff --git a/bundled_composition_contract_test.go b/bundled_composition_contract_test.go
new file mode 100644
index 0000000..85227d9
--- /dev/null
+++ b/bundled_composition_contract_test.go
@@ -0,0 +1,115 @@
+package promptkit_test
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+
+	"go.maximumdirect.net/configkit"
+	"go.maximumdirect.net/promptkit"
+)
+
+func TestBundledCompositionReplacementAndInheritance(t *testing.T) {
+	underlay := configkit.Input{Source: configkit.Mapping("caller underlay", map[string]any{
+		"profiles": []any{map[string]any{"id": "gpt-sol-latest", "model": "underlay-model"}},
+	})}
+	underlayEngine, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{Underlays: []configkit.Underlay{{Inputs: []configkit.Input{underlay}}}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	underlayProfile, err := underlayEngine.InspectProfile(context.Background(), "gpt-sol-latest")
+	if err != nil || underlayProfile.EffectiveModelParams.Model != "underlay-model" || underlayProfile.EffectiveModelParams.BackendID != "" {
+		t.Fatalf("underlay replacement = %+v, %v", underlayProfile, err)
+	}
+	main := configkit.Input{Source: configkit.Mapping("caller main", map[string]any{
+		"backends": []any{map[string]any{"id": "openrouter", "endpoint": "https://local.invalid/v1"}, map[string]any{"id": "other", "endpoint": "https://other.invalid/v1"}},
+		"profiles": []any{
+			map[string]any{"id": "gpt-sol-latest", "model": "main-model"},
+			map[string]any{"id": "custom", "extends": map[string]any{"id": "gpt-luna-latest"}, "model": "custom-model"},
+			map[string]any{"id": "auto", "backend": "other", "model": "other-model"},
+		},
+		"collections": map[string]any{"openrouter": map[string]any{
+			"backends": []any{map[string]any{"id": "local", "endpoint": "https://collection.invalid/v1"}},
+			"profiles": []any{map[string]any{"id": "profile", "backend": "openrouter/local", "model": "collection-model"}},
+		}},
+	})}
+	engine, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{Underlays: []configkit.Underlay{{Inputs: []configkit.Input{underlay}}}, Main: &main}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	inspect := func(id string) promptkit.ExecutionTarget {
+		t.Helper()
+		profile, err := engine.InspectProfile(context.Background(), id)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return profile.EffectiveModelParams
+	}
+	if target := inspect("gpt-sol-latest"); target.Model != "main-model" || target.BackendID != "" {
+		t.Fatalf("replacement = %+v", target)
+	}
+	if target := inspect("custom"); target.Model != "custom-model" || target.BackendID != "openrouter" || target.Endpoint != "https://local.invalid/v1" {
+		t.Fatalf("inherited = %+v", target)
+	}
+	if target := inspect("gpt-luna-latest"); target.Endpoint != "https://local.invalid/v1" || target.APIKeyEnv != "" {
+		t.Fatalf("backend replacement = %+v", target)
+	}
+	if target := inspect("openrouter/profile"); target.BackendID != "openrouter/local" || target.Model != "collection-model" {
+		t.Fatalf("collection = %+v", target)
+	}
+	for _, tier := range []string{"low", "medium", "high", "xhigh", "max"} {
+		target := inspect("auto-" + tier)
+		if target.BackendID != "other" || target.Model != "other-model" || !strings.Contains(fmt.Sprint(target.ExtraParams), "cost_tier:"+tier) || !strings.Contains(fmt.Sprint(target.ExtraParams), "id:auto-router") {
+			t.Errorf("tier %s = %+v", tier, target)
+		}
+	}
+}
+
+func TestBundledCompositionSequenceModes(t *testing.T) {
+	for _, test := range []struct {
+		name, mode, id string
+		wantErr        bool
+		count          int
+	}{
+		{"duplicate append", "append", "auto", true, 0},
+		{"distinct append", "append", "custom", false, 18},
+		{"replace", "replace", "custom", false, 1},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			input := configkit.Input{Source: configkit.Mapping("sequence", map[string]any{
+				"config":   map[string]any{"sequences": []any{map[string]any{"destination": []any{"profiles"}, "mode": test.mode}}},
+				"profiles": []any{map[string]any{"id": test.id, "model": "custom-model"}},
+			})}
+			engine, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{Main: &input}})
+			if test.wantErr {
+				if err == nil {
+					t.Fatal("expected duplicate rejection")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			profiles, err := engine.ListProfiles(context.Background())
+			if err != nil || len(profiles) != test.count {
+				t.Fatalf("profiles = %v, %v", profiles, err)
+			}
+		})
+	}
+}
+
+func TestBundledCompositionRejectsStrictConflictsAndMissingBackends(t *testing.T) {
+	profile := configkit.Input{Source: configkit.Mapping("profile", map[string]any{"profiles": []any{map[string]any{"id": "auto", "model": "caller"}}})}
+	_, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{Underlays: []configkit.Underlay{{Inputs: []configkit.Input{profile, profile}}}}})
+	if err == nil {
+		t.Fatal("strict group accepted duplicate records")
+	}
+	input := configkit.Input{Source: configkit.Mapping("replace backends", map[string]any{
+		"config":   map[string]any{"sequences": []any{map[string]any{"destination": []any{"backends"}, "mode": "replace"}}},
+		"backends": []any{map[string]any{"id": "other", "endpoint": "https://other.invalid/v1"}},
+	})}
+	if _, err := promptkit.NewEngine(promptkit.Config{Sources: promptkit.ConfigurationSources{Main: &input}}); err == nil {
+		t.Fatal("missing bundled backend was accepted")
+	}
+}
diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 00672e4..adfe228 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -183,6 +183,10 @@ Validation: targeted new composition tests plus existing source, inheritance,
 namespace, and profile-completion tests. Avoid reproducing ConfigKit's generic
 sequence implementation suite.
 
+Completion: facade integration tests cover caller precedence, whole-record
+replacement, inheritance, scoped resources, sequence modes, strict conflicts,
+and missing backend rejection. Targeted tests pass on Go 1.27.0.
+
 ## Stage 4: Verify Preparation And HTTP Request Construction
 
 Scope: bundled-profile execution integration with existing runner/client paths.